The invention relates to a rotating electrical machine and a system.
In ordinary industrial plants, a large part of compressor systems is installed on the ground, but gas plants include, for example, offshore plants and compressors used undersea. Also, some of compressors are operated in the ground 3000 m deep. Under such an environment, a rotating electrical machine used together with a compressor is required to be smaller and lighter. Because a high-power compressor system has to be installed in a limited installation space, it becomes essential to reduce a system scale including a compressor and a rotating electrical machine. The most effective method for reducing the scale of the whole system is, for example, to raise a rotational speed. In most cases, a rotational speed of an ordinary compressor system is that of a constant-speed machine, so that the rotational speed ranges from 1500 to 3600 rpm. To drastically reduce the system scale, it is needed to raise the rotational speed to about tens of thousands of rpm. Also, the speed-up of a rotating electrical machine for driving allows to eliminate a gearbox (speed-up gear) and to directly connect a rotating shaft of the compressor to a rotor of the rotating electrical machine.
When attempting the speed-up of a rotating electrical machine, a restriction is imposed, for example, on the size of a rotor diameter. Usually, dimensions of a rotor diameter and a shaft length are determined so that there is no problem with cooling and shaft vibration. However, the speed-up provides less flexibility to select the dimension of the rotor diameter. That is, the dimension of the rotor diameter has to be determined so that a circumferential velocity of the rotor does not exceed the sonic speed. Accordingly, if output power is increased, the shaft length is made long for that purpose. That is, a constitution of a rotating electrical machine having a higher rotational speed is inevitably made long in the axial direction. A problem caused when making long is a temperature distribution generated within the rotating electrical machine in the axial direction. Because a peak temperature is particularly generated near the center in the axial direction, it is necessary to positively cool a place near the center in the axial direction, thereby leveling the temperature distribution.
For cooling such an elongated, rotating electrical machine, various constructions thereof have been studied, and for example see JP-A-2013-090412, JP-A-2010-166816 and JP-A-2013-074654.
JP-A-2013-090412 discloses a construction in which a refrigerant blown from an axial flow fan within a rotating electrical machine provides a plurality of ventilation ducts disposed in a stator core in an axial direction, and a heat exchanger of the refrigerant and the stator core are held by a pressing plate so as to control the refrigerant to pass through an air gap between the stator pressing plate and a stator frame.
JP-A-2010-166816 discloses a construction in which a flow rate of a refrigerant is increased near the center in an axial direction by increasing the number of ventilation ducts disposed in a stator core, at the center in the axial direction and narrowing a distance between the ventilation ducts.
JP-A-2013-074654 discloses a construction in which ventilation paths having grooves of different depths from each other are formed on an outside diameter side of a stator core by laminating laminated steel plates in an axial direction, the plates of the stator core having different outside diameters from each other, and a ventilation duct is disposed in the axial direction of the stator core.